1. Field of the Invention
This invention relates to a power transmission mechanism for transmitting a driving force from at least one of an engine and an electric motor to drive wheels.
2. Description of the Prior Art
Conventionally, a power transmission mechanism of this kind has been proposed e.g. by Japanese Laid-Open Patent Publication (Kokai) No. 11-69509, which includes a multi-stage transmission for connecting an engine to a differential gear, and a clutch for connecting and disconnecting the multi-stage transmission to and from the engine. The multi-stage transmission has an output shaft directly connected to the drive shaft of a motor for driving drive wheels. When the power transmission mechanism performs a shifting operation during running of the vehicle being driven by the engine, the motor drives the output shaft of the multi-stage transmission immediately after disengagement of the clutch, thereby preventing occurrence of a sense of loss of a driving force during running of the vehicle (hereinafter referred to as an xe2x80x9cidle running feelingxe2x80x9d). Further, the motor performs regeneration during deceleration of the engine. The engine has a crankshaft thereof connected to an auxiliary machine-driving motor via an electromagnetic clutch and a belt transmission mechanism. This auxiliary machine-driving motor drives auxiliary machines, such as an air-conditioner compressor and the like, during stoppage of the engine.
For a hybrid vehicle incorporating the above conventional power transmission mechanism, at least two motors, that is, a motor for driving drive wheels and a motor for driving auxiliary machines are necessitated. In addition thereto, if a starter motor for starting the engine is separately provided, still another electric motor is necessitated, which leads to increased manufacturing costs of the vehicle and makes it difficult to secure a space for installing the mechanism in the vehicle. Further, since the motor for driving the drive wheels has a drive shaft thereof directly connected to the output shaft of the transmission, a relatively large torque is required to drive the drive wheels. This necessarily leads to an increased size of the motor, resulting in further increased manufacturing cost of the mechanism. Further, for the same reason, the drive wheel-driving motor offers an extra rotational resistance to the engine except when the drive wheels are being driven or the regeneration is being carried out. This results in degraded fuel economy.
It is an object of the invention to provide a power transmission mechanism for an automotive vehicle, which is capable of employing one electric motor as a drive source for driving drive wheels and as a drive source for starting an engine, thereby making it possible to reduce manufacturing costs of the vehicle, and preventing the motor from offering an extra rotational resistance when the drive wheels are being driven by the engine, thereby making it possible to improve fuel economy.
To attain the above object, the present invention provides a power transmission mechanism that connects at least one of an engine and an electric motor to drive wheels, thereby transmitting a driving force from the at least one of the engine and the electric motor to the drive wheels.
The power transmission mechanism according to the invention is characterized by comprising:
a multi-stage transmission including an input shaft connected to the engine and an output shaft connected to the drive wheels, the input shaft and the output shaft having a plurality of change gears arranged thereon which are selectively caused to mesh with each other, thereby transmitting the driving force from the engine to the drive wheels, such that a transmission gear ratio can be stepwise changed and at the same time the input shaft and the output shaft can be disconnected from each other, the multi-stage transmission having an input shaft gear and an output shaft gear fitted on the input shaft and the output shaft, respectively;
a drive shaft driven by the electric motor;
a first gear and a second gear arranged on the drive shaft; and
a switching mechanism for selectively switching a connection mode of the electric motor between an output shaft connection mode in which the electric motor is connected to the output shaft by meshing of the first gear with the output shaft gear, and an input shaft connection mode in which the electric motor is connected to the input shaft by meshing of the second gear with the input shaft gear.
According to this power transmission mechanism, the plurality of change gears selectively mesh with each other, whereby the driving force from the engine is transmitted to the drive wheels according to a transmission gear ratio between the meshed change gears, whereby the hybrid vehicle is driven for traveling. Further, when the connection mode of the electric motor is switched to the output shaft connection mode by the switching mechanism, the electric motor is connected to the output shaft via the first gear and the output shaft gear meshing with each other, and thereby connected to the drive wheels. As a result, the electric motor can be used as a drive source for driving the drive wheels, and even if the power transmission mechanism undergoes a shifting operation during running of the vehicle, the drive wheels can be driven by the electric motor, whereby it becomes possible to prevent occurrence of an idle running feeling. Further, when the connection mode is switched to the input shaft connection mode by the switching mechanism, the electric motor is connected to the input shaft via the second gear and the input shaft gear meshing with each other, and thereby connected to the engine. Consequently, when the output shaft and the input shaft are disconnected from each other during stoppage of the engine, it is possible to crank the engine by the electric motor. This enables the electric motor to be used as a starter motor. As described above, one electric motor can be employed as the drive source for driving drive wheels and as the drive source for cranking the engine, which not only makes it possible to reduce manufacturing costs of the vehicle but also makes it easy to secure a space for mounting the transmission mechanism in a hybrid vehicle. Further, since the electric motor has the first gear or the second gear meshing with the gear of the transmission, by exploiting gear ratios between these gears, the drive wheels can be driven with a torque smaller than that of the conventional electric motor which is directly connected to the output shaft of the transmission. This makes it possible to design the electric motor compact in size, thereby making it easy to secure a mounting space of the transmission mechanism in the vehicle.
Preferably, the input shaft gear is formed by an input shaft integrated gear integrally formed with the input shaft and an input shaft idle gear rotatable about the input shaft, the output shaft gear being integrally formed with the output shaft, the switching mechanism switching the connection mode of the electric motor to the output shaft connection mode by causing the first gear to mesh with the output shaft gear via the input shaft idle gear, and switching the connection mode to the input shaft connection mode by causing the second gear to mesh with the input shaft integrated gear.
According to this preferred embodiment, when the connection mode is switched to the output shaft connection mode by the switching mechanism, the first gear meshes with the output shaft gear via the input shaft idle gear, whereby the drive wheels are driven by the electric motor. Further, in the input shaft connection mode, the second gear meshes with the input shaft integrated gear, whereby the engine is cranked by the electric motor. In this case, generally, the transmission includes idle gears rotatable about the input shaft and the output shaft, and integrated gears as change gears, and hence if such existing change gears are employed as input shaft idle gears, input shaft integrated gears, and output shaft gears, the above effects can be obtained without adding extra gears other than the change gears. Further, since the electric motor and the drive shaft thereof can be arranged in parallel with the gear shafts of the transmission, lengths in the axial direction, such as the lengths of the input shaft and so forth, can be reduced as a whole, thereby ensuring excellent mounting performance of the hybrid vehicle.
Preferably the input shaft gear is integrally formed with the input shaft, the output shaft gear being formed by an output shaft integrated gear integrally formed with the output shaft and an output shaft idle gear rotatable about the output shaft, the switching mechanism switching the connection mode of the electric motor to the output shaft connection mode by causing the first gear to mesh with the output shaft integrated gear, and switching the connection mode to the input shaft connection mode by causing the second gear to mesh with the input shaft gear via the output shaft idle gear.
According to this preferred embodiment, in the output shaft connection mode, the first gear meshes with the output shaft integrated gear, whereby the drive wheels are driven by the electric motor. Further, in the input shaft connection mode, the second gear meshes with the input shaft gear via the output shaft idle gear, whereby the engine is cranked by the electric motor. Further, for the same reason as described hereinabove, the above advantageous effects can be obtained without adding extra gears, and lengths in the axial direction, such as the lengths of the input shaft and so forth, can be reduced as a whole, thereby ensuring excellent mounting performance of the hybrid vehicle.
Preferably, the switching mechanism is capable of further switching the connection mode of the electric motor to a cut-off mode in which the electric motor is disconnected from both the output shaft and the input shaft.
According to this preferred embodiment, when the connection mode is switched to the cut-off mode, the electric motor is disconnected from the output shaft and the input shaft, so that it is possible to prevent the electric motor from offering an extra rotational resistance when the drive wheels are being driven by the engine, thereby making it possible to enhance fuel economy.
Preferably, the electric motor is capable of performing regeneration operation, the transmission further including a reverse gear capable of simultaneously meshing with one of the change gears of the input shaft and one of the change gears of the output shaft, the transmission mechanism further including a clutch for disconnecting the transmission from the engine when the reverse gear simultaneously meshes with the one of the change gears of the input shaft and the one of the change gears of the output shaft, and the switching mechanism switches the connection mode of the electric motor to the input shaft connection mode, in a state in which the transmission and the engine are disconnected from each other by the clutch.
According to this preferred embodiment, when the reverse gear simultaneously meshes with one of the change gears of the input shaft and one of the change gears of the output shaft, the switching mechanism switches the connection mode to the input shaft connection mode in a state in which the transmission and the engine are disconnected from each other by the clutch, whereby the electric motor and the input shaft are connected to each other. Therefore, the electric motor offers a rotational resistance to the input shaft to thereby reduce the rotation of the input shaft, and hence when the reverse gear is caused to simultaneously mesh with the one of the change gears of the input shaft and the one of the change gears of the output shaft so as to change the traveling mode of the vehicle from a forward one to a backward one, the rotation of the input shaft is reduced by inertia of energy, and the reverse gear in a stopped state is caused to mesh with the one of the change gears of the input shaft whose rotation is reduced. This makes it possible to prevent occurrence of a gear squeal. In this case, if the regeneration operation by the electric motor is additionally carried out, the rotation of the engine can be reduced in a shorter time period, whereby it is possible to prevent occurrence of a gear squeal, and recover regenerative electric power at the same time.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.